Various packing boxes are widely used with different shapes or materials. According to the assembling manner, the packing boxes can be divided into the fixed packing box and the demountable packing box. A fixed packing box can be used directly while storing objects. Since the fixed packing box occupies an unchangeable three-dimensional space, it is inconvenient for storing and transporting the fixed packing box. The conventional demountable packing box assembled by folding and pasting, will be damaged at a certain extent after the packing box is disassembled. Therefore, it can not be reused, which adversely affects the cost of production and use. Moreover, it is required to solve some technical problems of the conventional demountable packing box, particularly to increase the convenience and stability of assembling and using.